The present invention relates to rotary drill bits having a plurality of conically shaped rotary cutters wherein each of the rotary cutters is supported in an outer roller bearing facing the drill bit body and at least one inner roller bearing on a trunnion projecting from the drill bit body. Rollers of the inner roller bearing run in a radial deep bearing race groove formed in the trunnion and in a deep bearing race groove formed in the bore of the rotary cutter for example, by machining. The rollers are inserted through a generally axially extending filling hole or elongated port in the trunnion between the two bearing race grooves.
Rotary drill bits of the type to which the present invention relate are not new per se. For example, rotary drill bits have been proposed in the past wherein the outer roller bearing facing the drill bit body comprises a cylindrical roller bearing wherein the cylindrical rollers are inserted through the filling hole of the inner roller bearing; that is, together with the rolling elements of the inner roller bearing. This type of assembly is shown in German Published Application No. 2,841,971. This type of rotary cutter has several disadvantages and drawbacks. For example, the rotary drill bit requires an inner bearing having the capability of withstanding extremely high axial forces by reason of the fact that extremely high axial forces of the conical rotary cutter occur in many applications and these forces are quite difficult to accommodate as a result of the inwardly tapering diameter of the rotary cutter. Furthermore, it has been observed that in inner roller bearing which takes the high axial forces developes increased bearing friction heat and consequently runs at a relatively high temperature since the heat generated near the tip of the rotary cutter during operation produced by cutter bore and bearing friction cannot always dissipate quickly enough to the ambient environment or to the drill bit body.
Furthermore, in these prior rotary drill bits, the rolling elements of the inner bearing which take up axial load are difficult to insert between the rotary cutter and trunnion when it is desired to insert the maximum number of rolling elements without a cage at the periphery of the trunnion in order to obtain a high axial load bearing capacity. Finally, in the prior rotary drill bits, the bearing race of the outer bearing facing the drill bit body is interrupted by the filling hole needed for inserting the rolling elements and insertion of the filler piece. Accordingly, this bearing race has a reduced bearing capacity at the location of the filling hole.
With the above in mind, it is an object of the present invention to provide a rotary drill bit characterized by novel features of construction and arrangement which can effectively withstand extremely high axial forces in addition to radial loads with only a moderate normal elevation in the operating temperature of the roller bearings.
It is a further object of the present invention to provide a rotary drill bit which is of compact and strong construction and is capable of being manufactured economically.
In the rotary drill bit according to the present invention, the roller bearing at the side of the drill bit body which transmits the axial load, is located at the end of the rotary cutter with the largest diameter. Consequently, a large number of rolling elements can be accommodated at the periphery which run in a bearing race uninterrupted, for example, by a filling hole in the trunnion, and in the bore of the rotary cutter. In this way the outer roller bearing provides maximum radial and axial load bearing capacity. By this arrangement, the roller bearing is especially adapted and suitable for taking up the operating pressures of the rotary cutter directed toward the drill bit body. Additionally, by this arrangement, the bearing friction heat developed in the outer roller bearing can be readily dissipated by convection or heat conductivity to the ambient environment or to the adjacent drill bit body.
Further, in accordance with the present invention, the inner roller bearing is incorporated in the rotary cutter in a manner so that the rolling elements run in deep radial race grooves of the trunnion and the rotary cutter and consequently securely hold the rotary cutter in place against accidental removal from the trunnion. The rotary drill bit of the present invention is therefore comprised of few components and the assembly of the rotary cutters to the trunnion of the drill bit body can be accomplished rather economically.
Other features of the invention, include the arrangement of conical rollers of the outer bearing which run on a conical bearing race in the bore of the rotary cutter with their cone angle corresponding to the shape of the outer contour of the conical rotary cutter. Consequently, in this manner the wall of the rotary cutter over the length of the bearing is of uniform thickness and consequently, a compact outer roller bearing which optimally utilizes the space in the rotary cutter is provided. Additionally, a rigid, break-resistant trunnion results since the conical bearing race of the tapered or conical rollers on the trunnion increase in diameter towards the drill bit body.
Note also that the tapered rollers run directly on the trunnion of the drill bit body and directly in the bore of the rotary cutter to minimize construction costs by maintaining the number of structural elements to a minimum.
In accordance with another feature of the present invention, the rotary cutter includes a circumferentially extending guide flange or shoulder formed integrally with the cutter and providing a guide surface against which the tapered rolling elements engage. The fixed shoulder for axially guiding the conical rollers is desirable since it cannot be loosened or detached even with high impact loads occurring in heavy operations.
The rotary drill bit assembly includes an inner roller bearing comprised of cylindrical rollers providing a radial bearing capacity and which is very easy to install and optimally utilizes the limited space available between the rotary cutter and the trunnion.